The present invention relates to a method and apparatus for forming a film on an object to be processed, such as a semiconductor wafer.
In general, in the manufacturing process of a semiconductor device, such as a semiconductor IC circuit, in order to form an interconnect pattern on one surface (major surface) of a semiconductor wafer constituting a to-be-processed object or bury a conductive material in a hole in an insulating film between interconnect lines, or achieve both, a metal or metallic compound, such as Al (aluminum), W (tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride) and TiSi (titanium silicide) is deposited to form a thin film.
Though, conventionally, aluminum has been mainly used as such a thin film material due to its easier manufacturing process, there is a recent tendency that, in place of aluminum, tungsten has been mainly used so as to achieve further microminiaturization and higher multi-layered structure or meet a high speed operation requirement. In order to improve an intimate contact with an underlying layer in the case of forming a tungsten film or to suppress the drawing up of Si atoms in the case where the Si atoms are included in the underlying layer, a TiN film for example is formed as a barrier metal film on the underlying surface and, by doing so, the tungsten film is deposited.
With reference to FIGS. 6A and 6B, an explanation will be made below about the film formation step at that time. In these Figures, the reference letter W shows a semiconductor wafer comprised of, for example, an Si substrate. The term xe2x80x9csemiconductor waferxe2x80x9d used in the present invention is referred to as a semiconductor wafer alone or a semiconductor wafer with one or more required films formed on its surface. As shown in FIG. 6A, prior to forming a tungsten film on a major surface of a wafer W, a barrier film 2 comprised of a TiN film is deposited as an underlying film on the wafer. Then, a tungsten film 4 of a given thickness is deposited on the barrier metal film 2 as shown in FIG. 6B. In general, the barrier metal film 2 may be formed under a low pressure of a few Torrs with the use of a sputtering film forming method or thermal CVD (Chemical Vapor Deposition) method and, in order to enhance the manufacturing efficiency, the wafer is placed simply on a susceptor within a film forming apparatus and film forming processing is carried out without the wafer being fixed to the susceptor by a clamping ring, etc. Therefore, the barrier metal film 2 is formed not only on an intended one surface or major surface of the wafer W but also, as shown by the reference numeral 2A, on a not-intended curved side face W2 of the wafer, or, as the case may be, on the reverse surface portion W3 of the wafer. Since, on the other hand, the formation of the tungsten film 4 has to be made at a fairly higher pressure of 80 Torrs than the above mentioned pressure, there is a risk that, unlike the film formation of the barrier metal film 2, the wafer W will be displaced on the susceptor during the film formation. Therefore, the film formation processing is done by abutting a link-like clamping ring 6 against a whole peripheral edge area of the upper surface of the wafer W. In this case, the flowing of a film forming gas around the side face W2 and reverse surface portion W3 of the wafer W is suppressed by the abutting clamping ring 6. Thus, the tungsten film 4 is deposited on the major surface W1 only of the wafer W, that is, on the barrier metal film at an area surrounded with the clamping ring, and not deposited on the side face W2 and reverse surface portion W3. That is, the tungsten film is deposited on the barrier metal film portion on the intended major surface of the wafer.
As set out above, the barrier metal film portion 2A deposited on the side face W2 and reverse surface portion W3 is peeled off or separated from the wafer at a later process step or steps, thus presenting a xe2x80x9cparticle generationxe2x80x9d problem.
It is accordingly the object of the present invention is to provide a method and apparatus for forming a film on a to-be processed object which can effectively eliminate any unwanted underlying film deposited on a side face and adjacent reverse surface portion of the object.
In one aspect of the present invention there is provided a method for forming a film, comprising: forming an underlying film on a major surface of a to-be-processed object and on a side face and adjacent reverse surface of the object, at least that side face; forming a main film on that portion of the underlying film portion corresponding to the major surface of the object; and etching the underlying film portion while leaving a given underlying film portion beneath the main film with the use of the main film as a mask.
By performing etching with a main film, that is, a main film formed on an underlying film, used as a mask it is possible to etch away an unwanted underlying film deposited on a side face and, if any, an adjacent reverse surface portion.
In this case, it is unavoidable that the main film serving as the mask has its upper surface portion slightly etched away and, as recited in claim 2, at the main film step for example, the main film is formed to a thickness greater than a target value by an extent corresponding to the etched-away amount of the main film at a later side-face etching step.
Even in this case, it is possible to etch away an unwanted underlying film deposited on a side face (and adjacent reverse-surface portion) of the object.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.